Long-term storage shapes ejaculate traits in a monogamous stingless bee (Scaptotrigona aff. depilis)

Abstract

The influence of long-term storage on the evolution of social insect male ejaculates remains a puzzle. Here, we studied the influence of sperm storage on male ejaculates in the stingless bee Scaptotrigona aff. depilis, a species where queens mate with a single male and thus do not trigger sperm competition. We estimated quantitative genetic parameters by sampling males from six colonies and two consecutive generations (n = 172). Heritability for sperm length was lower than heritability estimates for other traits. Coefficients of additive genetic variance (CVa) suggest sperm viability and sperm counts are under directional selection, sperm length under stabilizing selection, and male size under weak selection. Both genetic and phenotypic correlations were weak and not significant, indicating independent trait evolution. Overall, our findings provide evidence of selection acting on social insect ejaculates and bring insights for stingless bee breeding programs.